Typical oilfields are connected to thousands of miles of distribution pipelines that collect crude oil extracted from wellhead pumpjacks, gather the oil for measurement and accounting, and ultimately send it to refineries. A system of pumps is responsible for transporting oil from the wellhead through the complex pipeline system. The above-ground pipelines travel thousands of miles, oftentimes cross several countries and states, and therefore collectively undergo a variety of environmental conditions.
In cold weather, oil thickens because oil viscosity has an inverse relation with its temperature. That is, the viscosity of oil increases as its temperature decreases. As a result of oilfield environments having low ambient temperatures, pipelines can become blocked due to the high viscosity of oil. Such cold-oil pipeline blockage occurs gradually over time. Oil may also interact with sand or other contaminants in the fluid and with pipe sags or narrow fittings, blockages may result.
Typically, oil wells operate intermittently with on/off cycles of approximately 5-15 minutes, and when the pump is not operational, oil, in cold ambient temperatures, transitions from flowing slowly to fully blocking a pipe. Without having an indication of a pipeline block, the pump will continue to operate, thereby causing equipment damage and pump damage.
Accordingly, cold-oil blockage is a significant problem that occurs in complex oil pipeline distribution networks. Although some oilfields contain thousands of wells where production lines are vulnerable to blockage, manual inspection is the most commonly used technique today.
Further, although the oil industry has explored several stand-alone sensors, current approaches are either unreliable or too expensive to install and maintain. Other blockage sensing systems have attempted to locate blockages along an oil line by measuring the travel time of pressure decompression waves that bounce back from the blockage point. Other systems attempt to localize the blockage in subsea flow pipes by comparing inlet and outlet pressures. Such systems are invasive and expensive means for detecting blockages in pipes that do not address the blockage until after the blockage has occurred.